Catalytic process for the preparation of phosphazene polymers

ABSTRACT

A process is disclosed for the catalytically-induced preparation of phosphazene polymers. Cyclic halophosphazenes are polymerized in the presence of a catalytically sufficient amount of a compound having the formula M(OR&#39;) x  where M is an alkali metal or alkaline earth metal, x is equal to the valence of the metal and R&#39; is C 1  to C 10  linear or branched alkyl, C 1  to C 10  substituted linear or branched alkyl, the substituent selected from the group consisting of nitro, C 1  to C 10  alkyl, C 1  to C 10  alkoxy, C 6  to C 10  aryl and C 6  to C 10  aryloxy, or N 3  P 3  Cl z  (OR&#39;) 6-z  wherein R&#39; is as defined above and z equals 0 to 5. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a process for the preparation of phosphazene polymers. More specifically, the present invention relates to a method for catalytically producing polyphosphazenes. 
     DESCRIPTION OF THE PRIOR ART 
     Preparation of the polyphosphazenes has generally been recognized to be most readily accomplished by the technique of Allcock, et al as disclosed in U.S. Pat. No. 3,370,020. The preparation involves the use of the cyclic trimer, hexachlorocyclotriphosphazene as the sole starting material in what is essentially a melt polymerization technique. Purified trimer is thermally polymerized under sealed tube conditions at about 250° C. for 20 to 48 hours to give substantially linear poly(dichlorophosphazene) and some unreacted trimer. The cyclic tetramer also is effective in this reaction. While the product of this reaction, poly(dichlorophosphazene), itself is a good elastomer of very high molecular weight, e.g. over one million, it suffers the severe disadvantage of undergoing relatively facile hydrolytic cleavage of the P-Cl bond followed by degradation of the polymer. The prior art has shown that attempts to increase the stability of the dichloropolymer by continued heating have proved ineffective since the highly crosslinked rubbery material produced by such heating is also hydrolytically unstable. Recent success for obtaining polyphosphazene polymers of good hydrolytic stability has been achieved by substituting all of the halogen on the linear polymer produced from the cyclic trimer by various organic species. The following scheme discloses the state of the prior art to date in which high molecular weight polyphosphazenes are produced by treating poly(dichlorophosphazene) I with a variety of organic nucleophiles, e.g. alcohols, phenols, and amines, to obtain the corresponding completely substituted polymers II, III and IV which are hydrolytically stable. ##STR1## 
     The time period for accomplishing the ring opening polymerization reaction is economically disadvantageous, and considerable effort has been expended ascertaining what catalysts could be employed to successfully promote such ring opening polymerization. A variety of investigators have found that carboxylic acids, ethers, ketones, alcohols, nitromethane and metals such as zinc, tin or sodium, enhance the rate of polymerization of the cyclic trimer. The rate of enhancement is such that extensive polymerization is induced in 24 hours at 210° C. compared to only 3% conversion to polymer in the same time in the absence of any catalyst. Comparable catalytic activity has also been shown by sulfur (at 215°-254° C.), by dialkyl paracresols and quinone or hydroquinone. See, for example, Allcock, &#34;Phosphorus Nitrogen Compounds&#34;, Academic Press 1972, page 316 and following. 
     The mechanism proposed for such catalytic enhancement in the conversion of the cyclic trimer to the linear polymer suggests that reagents that facilitate removal of chloride ion from phosphorus should be active catalysts. However, a variety of compounds, including those that should be good chloride acceptors, have been found to have no effect on the polymerization including carbon tetrachloride, chloroform, ligroin, benzene, biphenyl, cyclohexane, ethylbromide, phosphorus pentachloride, ammonia, water, mercuric chloride, aluminum chloride and stannic chloride. 
     While the earlier discussed catalysts are effective for the purpose of catalyzing the ring-opening polymerization reaction, one of their major drawbacks is that the polymerization actually promotes the crosslinking reaction. Thus, while the disappearance of the cyclic trimer is enhanced, the resulting crosslinked polymer not only suffers the disadvantages of the prior art hydrolytically unstable crosslinked polychlorophosphazene V, but is additionally less reactive to the earlier mentioned nucleophiles due to its inherent insolubility. Further, there is no effective way to control molecular weight of the final product, such being so high as to make difficult any further manipulation such as melt or solution casting. 
     There is, therefore, a need for effective catalysts to produce linear polyphosphazenes. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a novel process for the production of phosphazene polymers. 
     It is a further object of the present invention to provide a novel process for the production of phosphazene polymeric foams. 
     It is an additional object of the present invention to provide a novel process for the production of low molecular weight phosphazene polymers and foams from such low molecular weight polyphosphazenes. 
     It is another object of the present invention to provide a novel process for the production of low molecular weight phosphazene polymers and foams from such low molecular weight polyphosphazenes which comprises thermally polymerizing a cyclic phosphazene with a catalytically sufficient amount of an alkali or alkaline earth metal compound. 
     It is a further object of the present invention to provide a novel process for the production of low molecular weight phosphazene polymers and foams therefrom which comprises thermally polymerizing a cyclic phosphazene with a catalytically sufficient amount of an alkoxy-substituted cyclotriphosphazene.

These and other objects of the present invention will become moreapparent to those skilled in the art upon reading the more detaileddescription thereof set forth hereinbelow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Extensive testing of a large variety of alkali metal, alkaline earthmetal, organo metallic and organic catalysts in cyclic phosphazenesystems has disclosed that while they vary somewhat in their activity,all the catalytically active compounds, in accordance with the presentinvention, have alkoxide character. By the term "alkoxide character" ismeant catalysts formed of radicals wherein an oxygen atom is attacheddirectly to another group to form a radical of the general formula

    (R'O--

wherein R' is linear or branched alkyl radical having from 1 to 10carbon atoms or substituted linear or branched alkyl radical having from1 to 10 carbon atoms, the substituents being halogen, nitro, C₁ to C₁₀alkyl, C₁ to C₁₀ alkoxide, C₆ to C₁₀ aryl or C₆ to C₁₀ aryloxy.Preferably R' is alkyl having from 1 to 4 carbon atoms, such beinglinear or branched.

In one embodiment of the present invention, the radical R' is combinedwith an alkali or alkaline earth metal M to form the catalytic compound

    M(OR').sub.x

wherein M is any Group I or II metal of the Periodic Table such aslithium, sodium, potassium, magnesium, or calcium, and x is equal to thevalence of the metal. For the sake of simplicity, these catalysts willhereinafter be referred to as metal alkoxide catalysts. Accordingly, thephosphazene polymers can be prepared by a one-step process in which themetal alkoxide catalyst is admixed with a cyclic compound of the formula

    (NPCl.sub.2).sub.y

wherein y is 3, 4, or mixtures of 3 and 4 and thermally polymerized.

It is preferred to carry out the catalytically-induced thermalpolymerization by heating the phosphazene compound at a temperature andfor a length of time ranging from about 5 hours at 250° C. to about 400hours at 140° C., preferably in the absence of oxygen and mostpreferably in the presence of a vacuum of at least 10⁻¹ Torr. That is tosay, the compounds are heated to a temperature ranging from about 140°C. to 250° C. for about 5 hours to 400 hours, the higher temperaturesnecessitating shorter contact times and the lower temperaturesnecessitating longer contact times. At temperatures higher than 250° C.,i.e. 300° C., crosslinking of the ring-opened material becomessignificant in these catalyzed systems. The compounds must be heated forsuch a length of time that only a minor amount of unreacted chargematerial remains and a major amount of polymeric non-cross-linkedmaterial has been produced. Such a result is generally achieved byfollowing the conditions of temperature and contact time as specifiedabove. Preferably, temperatures of 175°-250° C. are employed at times of5 to 300 hours.

While the ring-opening polymerization is most advantageously carried outin the melt phase, a judicious selection of solvents can also beemployed so as to effect the reaction in solution. However, thereactivitiy of the cyclic phosphazenes with materials having availableprotons is well known and the common hydrocarbon solvents, such asbenzene and the like, or the high boiling solvents, such as diglyme,dimethylformamide and the like, should be avoided. When solvents areused in the ring-opening polymerization, such should be inert to anyreaction with the cyclic phosphazene at the temperature ofpolymerization and are preferably polyhalocarbon solvents such as carbontetrachloride, perchloroethylene and various solvents generallydescribed as Freon solvents, but such having no available hydrogen atomspresent in the molecule.

It is preferred that the catalytically-induced thermal polymerization becarried out in the presence of an inert gas such as nitrogen, neon,argon, or in a vacuum of less than about 10⁻¹ Torr, inasmuch as thereaction proceeds very slowly in the presence of air. The use of anyparticular inert gas, however, is not critical.

The polymers resulting from the thermal polymerization portion of thisprocess are in the form of a polymeric mixture of different polymers ofdifferent chain lengths. That is to say, the product of the thermalpolymerization is a mixture of polymers having the formula

    --NPCl.sub.2 --.sub.n

wherein n ranges from about 6 to about 11,000. The recovered polymercontains phosphazene polymer, preferably having a weight averagemolecular weight of from about 60,500 to about 180,000, as well as someunreacted starting material. The recovered polymer is, however, actuallya mixture of polymers, generally having a molecular weight distributionthat is commonly termed bimodal, i.e., having two statistical modes.Thus, in these catalytically-induced thermally polymerized polymers, therecovered polymers have weight average molecular weights of about 6,000to 33,000 for the low molecular weight mode and about 60,000 to 230,000for the high molecular weight mode.

The amount of catalyst capable of carrying out the thermalpolymerization can be very small, the minimum amount being 0.05 molepercent based on the amount of cyclic phosphazene. It is important,however, that excessive amounts of catalyst not be used in thecatalytically-induced polymerization reaction. If amounts greater than10.0 mole percent, based on cyclic phosphazene, are employed in thepolymerization reaction, polymerization occurs but yielding highlycrosslinked phosphazene compounds. That is to say, a range of from about0.05 to about 10.0 mole percent is useful to induce the thermalpolymerization of phosphazene cyclic trimer, tetramer, or mixturesthereof, preferably from 0.5 to 2.0 mole percent.

Examples of the alkali or alkaline earth metal alkoxides which areuseful in the process in accordance with the present invention include:

sodium methoxide

potassium methoxide

sodium octyloxide

lithium octyloxide

potassium octyloxide

magnesium methoxide

magnesium octyloxide

calcium methoxide

calcium octyloxide

sodium decyloxide

lithium decyloxide

potassium decyloxide

magnesium decyloxide

calcium decyloxide

sodium chloromethoxide

lithium chloromethoxide

potassium chloromethoxide

calcium chloromethoxide

magnesium chloromethoxide

sodium ortho, meta, or para benzyloxide

potassium n-butoxide

lithium propoxide

calcium ethoxide

sodium ethoxide

lithium-1-methoxyethoxide

sodium-3-t-butoxyoctyloxide

lithium methoxymethoxide

magnesium-4-cyanohexoxide

sodium-8-nitrooctyloxide

potassium-10-nitrodecyloxide

calcium nitromethoxide

sodium iodomethoxide

sodium bromomethoxide

magnesium-10-iodooctyloxide

potassium-8-iodooctyloxide

calcium-6-bromooctyloxide

potassium-2-chlorooctyloxide

potassium-3-chlorooctyloxide

magnesium chloromethoxide

sodium-1-naphthylmethoxide

potassium-2-naphthylmethoxide

and the like. In another embodiment in accordance with the presentinvention, the catalytic compounds having alkoxide character, e.g.,having the group (R'O-- are those cyclotriphosphazenes of the formula

    N.sub.3 P.sub.3 Cl.sub.z (OR').sub.6-z

where z equals 0 to 5 and R' is as defined above. The synthesis of thesecatalytic compounds is well known in the prior art, such being describedin Inorg. Syn. VIII, page 77. In general, the preparation of thesecatalytic materials is carried out by reacting in an organic inertsolvent solution hexachlorocyclotriphosphazene with a metal alkoxide atabout 0° C. The following equation illustrates this reaction for thefully substituted product:

    (NPCl.sub.2).sub.3 + 6NaOR' → [NP(OR').sub.2 ].sub.3 + 6NaCl

wherein R' is as defined above.

As in the case of the metal alkoxide catalysts, those phosphazenecatalysts are effective in the thermal polymerization at concentrationsof as little as 0.05 mole percent. These alkoxide catalysts have anupper limit that is somewhat lower than the metal alkoxide catalystspractically useful in effecting the polymerization reaction. Thus,concentrations of up to 5.0 mole percent are effective for thepolymerization reaction in accordance with this embodiment of thepresent invention. Preferably from 0.05 to 2 mole percent are used forthe polymerization process, most preferably 0.1 to 0.5 mole percentbased on concentration of cyclic trimer or tetramer.

The exact phenomenon which occurs when polymerizing the cyclicphosphazene starting material used to produce the phosphazene polymersin accordance with the present invention is not completely understood.It is known, however, that the initiation step in the polymerization of(NPCl₂)_(y) wherein y is 3 or 4 is the heterolytic cleavage of aphosphorus-chlorine bond to produce a cyclic phosphazene cation inaccordance with the following equation. ##STR2## Cation (VI) thenelectrophilically attacks a neutral (NPCl₂)_(y) molecule, cleaving itsring and commencing the propagation step in the polymerization reactionas follows: ##STR3## While we do not wish to be bound by any explanationof the catalytically-induced thermal polymerization mechanism or theoryin regard thereto, it is possible that the catalysts in accordance withthe present invention are those which facilitate the formation of acyclic cation initiator, that is, other reagents that are similar to(VI) but which form more readily than do cyclic cation (VI). Thus, bysuch reasoning, a class of additives which function in this manner wouldbe those cyclic oxyphosphazanes (VIIIA) which form by a thermalrearrangement of the corresponding cyclophosphazenes (VII) in thefollowing manner: ##STR4## Oxyphosphazanes can also be formed from(NPCl₂)₃ by the following equation. ##STR5## Both phosphazane VIIIA andVIIIB can thermally cleave to zwitterions (IX) to effect the initiatorspecies similar to that accepted as the initiator species in theuncatalyzed thermal polymerization of (NPCl₂)_(y) raw materials.##STR6##

As a second step in the process in accordance with the presentinvention, thermally stable, water-resistant phosphazene polymerssubstantially free of halogen are produced from the above-mentionedcatalytically formed phosphazene polymer by reaction with specificreagents. These reagents have the formulas:

    M(OC.sub.6 H.sub.4 --R.sub.1).sub.x,

    M(OC.sub.6 H.sub.4 --R.sub.2).sub.x,

and, if desired,

    M(W).sub.x

wherein M is a Group I or Group II metal of the Periodic Table such aslithium, sodium, potassium, magnesium or calcium, x is equal to thevalence of the metal M, and R₁ and R₂ can be the same or different andare alkyl radical having from 1 to 10 carbon atoms, alkoxy having from 1to 4 carbon atoms, aryl radical having from 6 to 10 carbon atoms,substituted C₁ to C₁₀ alkyl radical or substituted C₆ to C₁₀ arylradical, the substituents being halogen, nitro, cyano, C₁ to C₄ alkyl,C₁ to C₄ alkoxy, C₆ to C₁₀ aryl, or C₆ to C₁₀ aryloxy radicals. The Wrepresents a group capable of crosslinking chemical reaction, such as,an olefinically unsaturated, preferably ethylenically unsaturated,monovalent radical containing a group capable of further reaction atrelatively moderate temperatures and the ratio of W:R₁ + R₂ is less thanabout 1:5. For the sake of simplicity, when copolymers are referred toherein, these may be represented by the formula [NP(OC₆ H₄ R₁)_(a) (OC₆H₄ R₂)_(b) (W)_(c) ]_(n) wherein W, R₁, R₂, and n are as set forth aboveand wherein a + b + c = 2 and c≧0. When c=0, a + b = 2. Examples of Ware --OCH═CH₂ ; --OR₃ CH═CH₂ ; --OC(R₃)═CH₂ ; OR₃ CF═CF₂ and similargroups which contain unsaturation, wherein R₃ is any aliphatic oraromatic radical, especially C₂ to C₁₀ alkylene. These groups arecapable of further reaction at moderate temperatures (for example,200°-350° F.) in the presence of free radical initiators, conventionalsulfur curing or vulcanizing additivies known in the rubber art or otherreagents, often even in the absence of accelerators, using conventionalamounts, techniques and processing equipment. Examples of free radicalinitiators include benzoyl peroxide, bis(2,4-dichlorobenzoyl peroxide),di-t-butyl peroxide, dicumyl peroxide,2,5-dimethyl(2,5-di-t-butylperoxy)hexane, t-butyl perbenzoate,2,5-dimethyl-2,5-di(t-butylperoxy)heptyne-3, and1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane. Thus, the generalperoxide classes which may be used for crosslinking include diacylperoxides, peroxyesters, and dialkyl peroxides.

Examples of sulfur-type curing systems include vulcanizing agents suchas sulfur, sulfur monochloride, selenium disulfide, tellurium disulfide,thiuram disulfide, p-quinone dioximes, polysulfide polymers, and alkylphenol sulfides. The above vulcanizing agents may be used in conjunctionwith accelerators, such as aldehyde amines, thio carbamates, thiuramsulfides, guanidines, and thiazols, and accelerator activators, such aszinc oxide or fatty acids, e.g., stearic acid.

It is also possible to use as W in the above formulas, monovalentradicals represented by the formulas (1) --OSi(OR⁴)₂ R⁵ and othersimilar radicals which contain one or more reactive groups attached tosilicon; (2) --OR⁶ NR⁶ H and other radicals which contain reactive --NHlinkages. In these radicals R⁴, R⁵ and R⁶ each represent aliphatic,aromatic and acyl radicals. Like those groups above, these groups arecapable of further reaction at moderate temperatures in the presence ofcompounds which effect crosslinking. The presence of a catalyst toachieve a cure is often desirable. The introduction of groups such as Winto polyphosphazene polymers is shown in U.S. Pat. Nos. 3,888,799;3,702,833; and 3,844,983, which are hereby incorporated by reference.

Aromatic substituted aryloxyphosphazene homopolymers, as disclosed inaccordance with the present invention, have higher smoke and lowerformability than alkyl substituted aryloxyphosphazene homopolymers.Similarly, in substituted aryloxyphosphazene copolymers, the ratio ofa:b and of (a+b):c in those copolymers containing W also affectsprocessability, smoke production and other physical properties. Forexample, it has been found that when R₁ and R₂ are the same and arearyloxy, highly crystalline polymers are formed which have higher smoke,and when compounded in foam compositions, show diminished foaming. WhenR₁ and R₂ are the same and are long alkyl chains, e.g. C₅ -C₁₀, aphosphazene homopolymer is formed that is soft, easily processed, andless crystalline than the aromatic homopolymers. Further, these polymersexhibit good foamability and low smoke. In the phosphazene copolymersherein (where R₁ and R₂ are different) and are, for example aryloxy andalkyl, respectively, the ratios of a:b and (a+b):c in copolymerscontaining W also affect processing properties, foamability and smoke.Thus, when the mole percent of R₂ as alkyl decreases, i.e. as more R₁aryloxy is substituted on the aryloxy group attached to the phosphazenechain, the amount of smoke increases, the processing becomes moredifficult and the foamability diminishes. It should be understood,however, that even the higher smoke, diminished foamability polymers andcopolymers, as disclosed herein, show lower smoke than prior artphosphazene polymers. When W is present, it has been found that when themole percent of W increases, the degree of crosslinking increases andthe ability to be foamed diminishes. Accordingly, it is contemplatedthat when copolymers are used in accordance with the present invention,and when R₁ or R₂ is alkoxy having from 1 to 8 carbon atoms, a moleratio of a:b of at least 1:6 and up to about 6:1, and preferably betweenabout 1:4 and 4:1, are used. It is also contemplated that the moleratios of c:(a+b) for copolymers or c:a in polymers where R₁ = R₂ willbe less than about 1:5, preferably from about 1:50 to about 1:10.

The second, or esterification, step of the process comprising treatingthe mixture resulting from the thermal polymerization step with acompound, or mixture of compounds having the formulas

    M(OR.sub.1).sub.x,

    M(OR.sub.2).sub.x,

and, if desired,

    M(W).sub.x

wherein M, x, R₁, R₂, and W are as specified above.

The polymer mixture is reacted with the above compound or mixture ofmetal compounds at a temperature and a length of time ranging from about25° C. for 7 days to about 200° C. for 3 hours.

Again, as in regard to the polymerization step mentioned above, thepolymer mixture is reacted with the alkali or alkaline earth metalcompound or compounds at a temperature ranging from about 25° C. toabout 200° C. for from about 3 hours to about 7 days, the lowertemperatures necessitating the longer reaction times and the highertemperatures allowing shorter reaction times. These conditions are, ofcourse, utilized in order to obtain the most complete reaction possible,i.e., in order to insure the complete conversion of all chlorine atomsin the polymer mixture to the corresponding ester of the alkali oralkaline earth starting materials.

The above esterification step is carried out in the presence of asolvent. The solvent employed in the esterification step must have arelatively high boiling point (e.g., about 115° C., or higher) andshould be a solvent for both the polymer and the alkali or alkalineearth metal compounds. In addition, the solvent must be substantiallyanhydrous, i.e., there must be no more water in the solvent or metalcompounds than will result in more than 1%, by weight, of water in thereaction mixture. The prevention of water in the system is necessary inorder to inhibit the reaction of the available chlorine atoms in thepolymer therewith. Examples of suitable solvents include diglyme,triglyme, tetraglyme, toluene and xylene. The amount of solvent employedis not critical and any amount sufficient to solubilize the chloridepolymer mixture can be employed. Either the polymer mixture or thealkaline earth (or alkali) metal compounds may be used as a solventsolution thereof in an inert, organic solvent. It is preferred, however,that at least one of the charge materials be used as a solution in acompound which is a solvent for the polymeric mixture.

The amount of alkali metal or alkaline earth metal compound or mixturesthereof employed should be at least molecularly equivalent to the numberof available chlorine atoms in the polymer mixture. However, it ispreferred that an excess of the metal compound be used in order toassure complete reaction of all the available chlorine atoms. Generally,for copolymers the ratio of the individual alkali metal or alkalineearth metal compounds in the combined mixture governs the ratio of thegroups attached to the polymer backbone. However, those skilled in theart readily will appreciate that the nature and, more particularly, thesteric configuration of the metal compounds employed may effect theirrelative reactivity. Accordingly, the ratio of R₁ 's and R₂ 's in theesterified product, if necessary, may be controlled by employing astoichiometric excess of the slower reacting metal compound.

Examples of alkali or alkaline earth metal compounds which are useful inthe process of the present invention include:

sodium phenoxide

potassium phenoxide

sodium p-methoxyphenoxide

sodium o-methoxyphenoxide

sodium m-methoxyphenoxide

lithium p-methoxyphenoxide

lithium o-methoxyphenoxide

lithium m-methoxyphenoxide

potassium p-methoxyphenoxide

potassium o-methoxyphenoxide

potassium m-methoxyphenoxide

magnesium p-methoxyphenoxide

magnesium o-methoxyphenoxide

magnesium m-methoxyphenoxide

calcium p-methoxyphenoxide

calcium o-methoxyphenoxide

calcium m-methoxyphenoxide

sodium p-ethoxyphenoride

sodium o-ethoxyphenoride

sodium m-ethoxyphenoride

potassium p-ethoxyphenoxide

potassium o-ethoxyphenoxide

potassium m-ethoxyphenoxide

sodium p-n-butoxyphenoxide

sodium m-n-butoxyphenoxide

lithium p-n-butoxyphenoxide

lithium m-n-butoxyphenoxide

potassium p-n-butoxyphenoxide

potassium m-n-butoxyphenoxide

magnesium p-n-butoxyphenoxide

magnesium m-n-butoxyphenoxide

calcium p-n-butoxyphenoxide

calcium m-n-butoxyphenoxide

sodium p-n-propoxyphenoxide

sodium o-n-propoxyphenoxide

sodium m-n-propoxyphenoxide

potassium p-n-propoxyphenoxide

potassium o-n-propoxyphenoxide

potassium m-n-propoxyphenoxide

sodium p-methylphenoxide

sodium o-methylphenoxide

sodium m-methylphenoxide

lithium p-methylphenoxide

lithium o-methylphenoxide

lithium m-methylphenoxide

sodium p-ethylphenoxide

sodium o-ethylphenoxide

sodium m-ethylphenoxide

potassium p-n-propylphenoxide

potassium o-n-propylphenoxide

potassium m-n-propylphenoxide

magnesium p-n-propylphenoxide

sodium p-isopropylphenoxide

sodium o-isopropylphenoxide

sodium m-isopropylphenoxide

calcium p-isopropylphenoxide

calcium o-isopropylphenoxide

calcium m-isopropylphenoxide

sodium p-sec butylphenoxide

sodium m-sec butylphenoxide

lithium p-sec butylphenoxide

lithium m-sec butylphenoxide

lithium p-tert. butylphenoxide

lithium m-tert. butylphenoxide

potassium p-tert. butylphenoxide

potassium m-tert. butylphenoxide

sodium p-tert. butylphenoxide

sodium m-tert. butylphenoxide

sodium propeneoxide

sodium p-nonylphenoxide

sodium m-nonylphenoxide

sodium o-nonylphenoxide

sodium 2-methyl-2-propeneoxide

potassium buteneoxide

and the like.

The second step of the process results in the production of ahomopolymer having the formula

    --NP(OC.sub.6 H.sub.4 R.sub.1).sub.2 --.sub.n

or a copolymer mixture having the formula

    --NP(OC.sub.6 H.sub.4 R.sub.1).sub.a (OC.sub.6 H.sub.4 R.sub.2).sub.b (W).sub.c --.sub.n

wherein n, R₁, R₂ and W are as specified above, where c, but not a and bcan be zero, and where a + b + c = 2, and the corresponding metalchloride salt. It should be noted herein that these polymers also havethe bimodal molecular weight distribution characteristic of theringopened, halogen-containing polymer.

The polymeric reaction mixture resulting from the second oresterification step is then treated to remove the salt which resultsupon reaction of the chlorine atoms of the polymer mixture with themetal of the alkali or alkaline earth metal compounds. The salt can beremoved by merely precipitating it out and filtering, or it may beremoved by any other applicable method, such as by washing the reactionmixture with water after neutralization thereof with, for example, anacid such as hydrochloric acid.

The next step in the process comprises fractionally precipitating thepolymeric material to separate out the high polymer from the low polymerand any unreacted trimer. The fractional precipitation is achieved bythe, preferably dropwise, addition of the esterified polymer to amaterial which is a non-solvent for the high polymer and a solvent forthe low polymer and unreacted trimer. That is to say, any material whichis a non-solvent for the polymers wherein n is higher than 350 and asolvent for the remaining low polymers may be used to fractionallyprecipitate the desired polymers. Examples of materials which can beused for this purpose include hexane, diethyl ether, carbontetrachloride, chloroform, dioxane, methanol, water and the like. Thefractional precipitation of the esterified polymeric mixture generallyshould be carried out at least twice and preferably at least four timesin order to remove as much of the low polymer from the polymer mixtureas possible. The precipitation may be conducted at any temperature,however, it is preferred that room temperature be employed. The novelhigh molecular weight polymer may then be recovered by filtration,centrifugation, decantation or the like.

The novel phosphazene polymers of this invention, as mentioned above,are very thermally stable. They are soluble in specific organic solventssuch as tetrahydrofuran, benzene, xylene, toluene, dimethylformamide andthe like and can be formed into films from solutions of the copolymersby evaporation of the solvent. Significantly, they are water resistantat room temperature and do not undergo hydrolysis at high temperatures.The polymers may be used to prepare films, fibers, coatings, moldingcompositions and the like. They may be blended with such additives asantioxidants, ultraviolet light absorbers, lubricants, plasticizers,dyes, pigments, fillers such as litharge, magnesia, calcium carbonate,furnace black, alumina trihydrate and hydrated silicas, other resins,etc., without detracting from the scope of the present invention.

The homopolymers and copolymers may be used to prepare foamed productwhich exhibit excellent fire retardance and which produce low smokelevels, or essentially no smoke when heated in an open flame. The foamedproducts may be prepared from filled or unfilled formulations usingconventional foam techniques with chemical blowing agents, i.e. chemicalcompounds stable at original room temperature which decompose orinteract at elevated temperatures to provide a cellular foam. Suitablechemical blowing agents include:

    ______________________________________                                                              Effective                                                                     Temperature                                             Blowing Agent         Range ° C                                        ______________________________________                                        Azobisisobutyronitrile                                                                              105-120                                                 Azo dicarbonamide(1,1-azobisform-                                             amide)                100-200                                                 Benzenesulfonyl hydrazide                                                                            95-100                                                 N,N'-dinitroso-N,N'-dimethyl tere-                                            phthalamide                                                                   Dinitrosopentamethylenetetramine                                                                    130-150                                                 Ammonium carbonate    58                                                      p,p'-oxybis-(benzenesulfonyl-                                                 hydrazide)            100-200                                                 Diazo aminobenzene    84                                                      Urea-biuret mixture    90-140                                                 2,2'-azo-isobutyronitrile                                                                            90-140                                                 Azo hexahydrobenzonitrile                                                                            90-140                                                 Diisobutylene         103                                                     4,4'-diphenyl disfulfonylazide                                                                      100;14 130                                              ______________________________________                                    

Typical foamable formulations include:

    ______________________________________                                        Phosphazene copolymer (e.g., [N P (OC.sub.6 H.sub.5) (OC.sub.6 H.sub.4        -p-OCH.sub.3)].sub.n                                                                                100 parts                                               ______________________________________                                        Filler (e.g., alumina trihydrate)                                                                     0-100   phr                                           Stabilizer (e.g., magnesium oxide)                                                                    2.5-10  phr                                           Processing aid (e.g., zinc stearate)                                                                  2.5-10  phr                                           Plasticizer resin (e.g., Cumar P-10,                                          coumarone indene resin) 0-50    phr                                           Blowing agent (e.g., 1,1'-azobisformamide)                                                            10-50   phr                                           Activator (e.g., oil-treated urea)                                                                    10-40   phr                                           Peroxide curing agent (e.g., 2,5-dimethyl-                                    2,5-di(t-butylperoxy)hexane)                                                                          2.5-10  phr                                           Peroxide curing agent (e.g., benzoyl                                          peroxide)               2.5-10  phr                                           ______________________________________                                    

While the above are preferred formulation guidelines, obviously some orall of the adjuvants may be omitted, replaced by other functionallyequivalent materials, or the proportions varied, within the skill of theart of the foam formulator.

In one suitable process, the foamable ingredients are blended togetherto form a homogeneous mass; for example, a homogeneous film or sheet canbe formed on a 2-roller mill, preferably with one roll at ambienttemperature and the other at moderately elevated temperature, forexample 100°-120° F. The homogeneous foamable mass can then be heated,to provide a foamed structure; for example, by using a mixture of acuring agent having a relatively low initiating temperature, such asbenzoyl peroxide, and a curing agent having a relatively high initiatingtemperature, such as 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, andpartially precuring in a closed mold for about 6-30 minutes at 200°-250°F., followed by free expansion for 30-60 minutes at 300°-350° F. In thealternative, the foaming may be accomplished by heating the foamablemass for 30-60 minutes at 300°-350° F. using a high temperature or lowtemperature curing agent, either singly or in combination. One benefitof utilizing the "partial precure" foaming technique is that an increasein the molecular weight of the foamable polymer prior to the foamingstep enables better control of pore size and pore uniformity in thefoaming step. The extent of "precure" desired is dependent upon theultimate foam characteristics desired. The desired foaming temperatureis dependent on the nature of the blowing agent and the crosslinkerspresent. The time of heating is dependent on the size and shape of themass being foamed. The resultant foams are generally light tan toyellowish in appearance, and vary from flexible to semirigid, dependingupon the glass transition temperature of the copolymer employed in thefoam formulation, that is to say, the lower the glass transition of thecopolymer the more flexible will be the foam produced therefrom. Asindicated, inert, reinforcing or other fillers such as aluminatrihydrate, hydrate silicas or calcium carbonate can be added to thecopolymer foams and the presence of these and other conventionaladditives should in no way be construed as falling outside the scope ofthis invention.

Also, as mentioned above, the homopolymers and copolymers of thisinvention can be crosslinked at moderate temperatures by conventionalfree radical curing techniques and in copolymers with minor amounts ofunsaturated groups W present in the copolymer backbone with conventionalsulfur curing techniques. The ability of these polymers to be cured attemperatures below about 350° F. makes them particularly useful aspotting and encapsulation compounds, sealants, coatings and the like.The copolymers are also useful for preparing crosslinked foams whichexhibit significantly increased tensile strengths over uncured foams.These copolymers are often crosslinked in the presence of inert,reinforcing or other fillers and the presence of these and otherconventional additives are deemed to be within the scope of thisinvention.

The following examples are set forth for purposes of illustration onlyand are not to be construed as limitations of the present inventionexcept as set forth in the appended claims. All parts and percentagesare by weight unless otherwise indicated.

EXAMPLE 1

To a 15 ml tared pyrex glass polymerization tube was added 0.0307 g.sodium methoxide, and 10.2 g. hexachlorocyclotriphosphazene which hadbeen purified by crystallization from heptane and distillation. Theconcentration of NaOCH₃ was, therefore, 0.3 weight percent or 1.9 molepercent. The above operations were carried out in a nitrogen-filled drybox. The tube containing the trimer and catalyst was connected to avacuum pump and evacuated for 30 minutes to 10⁻² Torr, then sealed whilestill under vacuum. The tube was then heated in an oven at 175° C. for312 hours, at which time the viscosity had increased until the materialwould barely flow when the tube was inverted at the reactiontemperature.

EXAMPLE 2

The poly(dichlorophosphazene) prepared in Example 1 was opened in thedry box and the contents dissolved in 150 ml toluene. The toluenesolution of (NPCl₂)_(n) was added dropwise to a stirred solution ofsodium p-isopropylphenoxide (previously prepared by the reaction of 4.8g, 0.208 moles sodium with 28.7 g, 0.211 moles p-isopropylphenol in 175ml diglyme). The reaction solution was then heated with stirring at 115°for 70 hours. After cooling to 85°, the reaction mixture was poured into1500 ml methanol to precipitate the polymer. After 2 hours stirring, themethanol was decanted, replaced with fresh methanol and allowed toremain for 65 hours. The methanol was then replaced with water andallowed to stand overnight. The water was poured off, the polymer rinsedin methanol and then dried under vacuum. The yield of dry polybis(p-isopropylphenoxy)phosphazene was 29% based on the originalhexachlorocyclotriphosphazene. After further purification by dissolvingin THF and precipitating into water and drying, GPC analysis showed abimodal molecular weight distribution with a Mw of 284,000 and a Mw/Mnvalue of 14.3. See Table, Example 2.

COMPARATIVE

A control sample of (NPCl₂)₃ without added catalyst, treated in the sameway as Example 1, showed no apparent increase in viscosity after 328hours at 175°, e.g. no ring-opening polymerization had occurred. SeeTable, Comparative.

EXAMPLE 3

Using the same procedure as in Example 1, hexaethoxycyclotriphosphazene(0.3 weight percent, 0.26 mole percent) was added to (NPCl₂)₃. The timerequired for polymerization was 145 hours at 175°. Thehexaethoxycyclotriphosphazene was prepared by the method of Fitzsimmonsand Shaw, Inorg. Syn. VIII, p. 77.

EXAMPLE 4

Using the same procedure as in Example 2, a toluene solution of the(NPCl₂)_(n) prepared in Example 3 was added to a solution of sodiump-isopropylphenoxide in diglyme. The yield of dry polymer was 21.7%.Analysis of purified polymer on GPC showed a bimodal molecular weightdistribution with Mw = 185,000 and Mw/Mn = 13.3. See Table, Example 4.

Other examples are illustrated in the following table. The procedureused in these illustrative examples is identical to that of Examples1-4.

                                      Examples 5-18                               __________________________________________________________________________    (NPCl.sub.2).sub.3 Ring Opening Polymerization                                                      Polymerization                                                                        (NPCl.sub.2).sub.n Substitution                               Concentration                                                                         Time                                                                              Temp.                                                                             Yield                                           Example                                                                            Catalyst Species                                                                       Mole %  Hours                                                                             ° C.                                                                       %   Mw.sup.a                                                                            Mw/Mn                                 __________________________________________________________________________          ##STR7##                                                                              1.90    312 175 29.0.sup.b                                                                        284,000                                                                             14.3                                  5    "        0.26    328 175 11.3.sup.b                                                                        501,000                                                                             17.6                                   6    "       3.80     62 175 29.7.sup.b                                                                        Not Determined                              7    "        0.50    234 200 24.9.sup.b                                                                        Not Determined                               8    "       1.00    100 200 23.3.sup.b                                                                        509,000                                                                             18.4                                   9    "       1.90     59 200 28.6.sup.b                                                                        Not Determined                              10   "        3.80    23  200 26.1.sup.b                                                                        Not Determined                              11   "        1.90    8   250 34.6.sup. b                                                                       Not Determined                              12    "       1.90     63 200 30.0.sup.c                                                                        213,000                                                                             11.4                                  4                                                                                   ##STR8##                                                                              0.26    145 175 21.7.sup.b                                                                        185,000                                                                             13.3                                  13    "       0.50     18 175 18.1.sup.b                                                                        Not Determined                              14   "        0.10    33  200  8.2.sup.b                                                                        Not Determined                              15    "       0.20     19 200 25.2.sup.b                                                                        316,000,                                                                            15.2                                  16    "       0.10    5.5 250 18.0.sup.b                                                                        Not Determined                              17    "       0.20     13 200 22.5.sup.d                                                                        343,000                                                                              8.2                                  18    "       0.50     11 200 17.0.sup.e                                                                        Not Determined                              Comparative   --      328 175 no polymerization                               "             --      464 200 no polymerization                                "            --      15.0                                                                              250 38.0.sup.b                                                                        1,450,000                                                                           42.5                                  __________________________________________________________________________     .sup.a by Waters Model #200 Gel Permeation Chromatograph                      .sup.b the reaction product of (NPCl.sub.2).sub.n with sodium                 p-isopropylphenoxide                                                          .sup.c the reaction product of (NPCl.sub.2).sub.n with sodium                 phenoxide/sodium p-sec butylphenoxide in the ratio of 1:1                     .sup.d the reaction product of (NPCl.sub.2).sub.n with sodium                 methoxyphenoxide/sodium p-isopropylphenoxide in the ratio of 1:1              .sup.e the reaction product of (NPCl.sub.2).sub.n with sodium                 p-methoxyphenoxide/sodium p-chlorophenoxide in a ratio of 1:1 having 3        mole % of the substitution 4-pentene-1-oxide                             

EXAMPLE 19

To 100 parts of the copolymer prepared in accordance with Example 18,there were added 100 parts of alumina trihydrate, 5 parts of magnesiumoxide, 10 parts of zinc stearate, 2 parts of CUMAR P-10(p-coumarone-indene resin), 20 parts of Celogen AZ(1,1'-azobisformamide), 5 parts of BIK-OT (an oil treated urea) as anactivator, 6 parts of 2,5-dimethyl-2,5-di(t-butyl peroxy)hexane, 2 partsof benzoyl peroxide (78% active), and 1 part of dicumyl peroxide. Theabove ingredients were milled to insure homogeneous mixing of allmaterials and were then precured in an open sided mold for 1 minute at210° F. under 2000 psi. The precured copolymer was then free expanded ina circulating air oven for 30 minutes at 300° F. The resultant foam waslight tan and flexible, having a foam density of 11.4 pounds/ft.³.

What is claimed is:
 1. The process for preparing a phosphazene polymer which comprises heating a cyclic compound of the formula (NPCl₂)_(y) where y is 3, 4, or mixtures thereof at 140°-250° in an inert atmosphere with a catalytically sufficient amount of a compound having the formula N₃ P₃ Cl_(z) (OR')_(6-z) wherein R' is C₁ to C₁₀ linear or branched alkyl, C₁ to C₁₀ substituted linear or branched alkyl, the substituent selected from the group consisting of halogen, nitro, C₁ to C₁₀ alkyl, C₁ to C₁₀ alkoxy, C₆ to C₁₀ aryl and C₆ to C₁₀ aryloxy radicals and z equals 0 to
 5. 2. The process in accordance with claim 1 wherein said thermal polymerization is carried out in an inert atmosphere for from 5 to 400 hours.
 3. The process in accordance with claim 1 wherein said cyclic compound is hexachlorocyclotriphosphazene or octochloro cyclotetraphosphazene.
 4. The process for preparing a phosphazene polymer which comprises heating hexachlorotriphosphazene at 140°-250° C. in an inert atmosphere with 0.05 to 5.0 mole percent of a compound having the formula N₃ P₃ Cl_(z) (OR')_(6-z), wherein R' is C₁ to C₁₀ linear or branched alkyl or C₆ to C₁₀ aryl-substituted C₁ to C₁₀ linear or branched alkyl and z is equal to 0 to
 5. 5. The process in accordance with claim 4 wherein said heating is at a temperature of from about 175° C. to about 250° C. for a time from about 5 hours to about 300 hours. 